This invention relates to a continuous process for galvanizing linear materials such as wire, rod, tube or pipe, by immersing the axially moving linear element incrementally in molten zinc.
The galvanization of the exterior surface of pipe or conduit as part of the continuous manufacture thereof from an endless strip of sheet metal has been practiced commercially for a number of years. The process basically consists of roll-forming the metal strip into tubular form after drawing it from an endless supply, welding the seam, scarfing and dressing off the weld, and passing the continuously formed tube through a pickling bath and rinse. The tube is then passed through a preheating station and then through a bath of molten zinc, after which the excess zinc is removed, the tube cooled to handling temperature in a water bath, and the tube sheared into finite lengths. The tube may be subjected to a sizing operation after being cooled, prior to the shearing operation.
Such an integrated continuous manufacturing process is disclosed, for example, in U.S. Pat. No. 3,226,817, with particular emphasis on the galvanization step of the process in U.S. Pat. Nos. 3,226,817, 3,259,148 and 3,877,975.
In the galvanizing stations of such prior integrated processes, the continuously-formed, rapidly moving tube, after appropriate preparation, was passed through an elongated trough positioned above a pool of molten zinc in a large vat, from which a stream of the liquid metal was pumped to maintain a substantial and overflowing body of molten zinc in the trough as well as to replace the zinc being carried away from the trough as a fluid coating on the tube.
As described in co-pending application Ser. No. 07/892,432, it has recently been found that coating of linear elements in a continuous galvanizing process may be effected by immersion of the linear elements in molten zinc in an open tube, with zinc flowing out of the opposite ends of the tube. This arrangement enables galvanizing to be accomplished with reduced zinc flow as compared with prior methods employing overflowing troughs. Reduction of zinc flow is generally desirable due to the consequent reduction of the corrosive and abrasive effects of molten zinc on pump components and other system components.